%!tikz editor 1.0
\documentclass{article}
\usepackage{tikz}
\usepackage[graphics, active, tightpage]{preview}
\PreviewEnvironment{tikzpicture}

%!tikz preamble begin
\usetikzlibrary{arrows,positioning,automata,shadows,shapes,snakes,patterns,decorations}
\usetikzlibrary{calc}
\usetikzlibrary{positioning}

%!tikz preamble end


\begin{document}
%!tikz source begin
\begin{tikzpicture}[
state/.style={draw, circle, fill=white,drop shadow={opacity=0.25},font=\sffamily\scriptsize, text width=1.6cm, text centered, minimum height=1.2cm},
transched/.style={dashed,->,bend right,thick,font=\sffamily,text centered},
tranapp/.style={solid,->,bend right,thick,font=\sffamily,text centered},
tranapp2/.style={solid,->,bend left,thick,font=\sffamily,text centered},
]
\node[state] (suspended) at (0,2.8) {SUSPENDED};
\node[state] (ready) at (-2.5,0) {READY};
\node[state] (running) at (2.5,0) {RUNNING};
\node[state] (waiting) at (0,-2.8) {WAITING};

\draw (suspended) edge [tranapp] node [left] {activate} (ready) ;
\draw (ready) edge [transched] node [below] {start} (running) ;
\draw (running) edge [transched] node [above] {preempt} (ready) ;
\draw (running) edge [tranapp] node [right] {terminate} (suspended) ;
\draw (running) edge [tranapp2] node [right] {block} (waiting) ;
\draw (waiting) edge [tranapp2] node [left] {release} (ready) ;

\end{tikzpicture}
%!tikz source end

\end{document}